766
SOAP.— Palm Oil Bleaching.
Castor-oil and spermaceti soaps are emollient, andespeciaily applicable to toilet purposes.
Palm-oil soap is little inferior to castor-oil or sper-maceti soap. When combined with rosin, it con-stitutes the well-known “ yellow soap.”
Lastly, soaps prepared from drying oils are usuallysoft and flabby.
The appended table shows the quantity of soapobtained from 3 lbs. of each of the oils mentionedabove, saponified with caustic soda solution.
Oil or Fat.
Quantity obtained astaken from the frame.
Loss of Weightin Lbs. and Ozs.
Time.
Olive oil,.
White,.
6 lbs. 10 OZS.
5 lbs, 0 OZ.
2 months.
Sweet almond, oil,.
White,.
5 “ 11 “
4 “ 6 “
2 months.
Colza oil,.
Lemon-yellow,.
5 “ 14 “
5 “ 0 “
15 days.
Rape-seed oil,.
Beech-nut oil,.
White.
6 “ 8 “
5 “ 0 “
20 days.
Dirty-grey,.
5 “
4 “
4 “ 13 “
2 months.
Poppy oil,.
Grey,.
4 “
8 “
4 “ 6 “
45 days.
Hemp-seed oil,.
Green,.
Deep yellow,.
5 “
0 “
4 “ 14 “
15 days.
Nut oil,.
4 “
7 “
4 “ 6 “
15 days.
Linseed oil.
Yellowish.
5 “
0 “
4 “ 12 “
1 month.
Sperm oil,.
Dirty-grey,.
4 “
12 “
4 “ 10 “
15 days.
Fish oil,.
Reddish-brown,.
4 “
11 “
4 “ 8 “
1 month.
Cod-liver oil,.
Dirty grey,.
4 “
14 “
4 “ 12 “
15 days.
Suet or tallow,.
White,.
8 “ 4 “
6 “ 0 “
2 months.
Lard,.
White,.
8 “ 3 “
5 “ 0 “
2 months.
Washed rancid butter,.
White,.
11 “
0 “
7 “ 0 “
2 months.
Palm Oil . —As it arrives in this country, this oilis tinged with a peculiar and characteristic orange-red colour, which renders it unfit for use for soapmaking in its natural state. This colouring matteris not proper to the pure oil, which in a state ofchemical purity is perfectly colourless. There isassociated with the oil, however, and extracted withit from the palm, a peculiar principle which in thecourse of time undergoes spontaneous decomposi-tion, assuming at the same time a characteristiccolour.
Numerous processes have from time to time beenadopted to effect the decoloration of palm oil,nearly all of which depend upon the applicationof nascent oxygen produced through the decom-position of various compounds, from which it maybe liberated with a greater or less degree of facility.
The old method consisted in the employment ofnitric acid, but this method has the disadvantageof impairing the peculiar violet odour of the oilupon which its value chiefly depends; whilst, at thesame time, though the colouring matter is destroyed,the oil is not perfectly bleached, and hence it yieldsa soap of a greyish-yellow hue. Neither is chlorinewell adapted for the purpose, though the colouringmatter is readily decomposed by it; for this agentexerts an injurious action on the oil itself, developinga brown tint, and impairing its consistence.
Of all methods of bleaching palm oil, the best isthat originally proposed and patented by Watt, inwhich the decoloring agent is nascent oxygen pro-duced by the decomposition of chromic acid. Theprocess is commenced' by heating the oil by steamin an ordinary boiling cauldron for half an hour; itis then allowed to stand at rest to deposit impurities,and when cooled down to about 130° Fahr., it isdrawn off from the sediment and condensed steam,and placed in wooden vessels, each capable of con-taining 2 or 3 tuns. To each half tun of oil, thusfreed from extraneous matters, the following mixtureis added:—A saturated aqueous solution of 12j lbs.of bichromate of potash, 4 lbs. of concentrated sul-
phuric acid, and about 25 lbs. of strong hydrochloricacid. These proportions are not always strictlyadhered to; many bleachers using to the abovequantity of oil 10 lbs. of the bichromate, and 40 ofthe hydrochloric acid. After being well agitatedwith the mixture for a few minutes, the oil becomes ofa black colour; in a short time, however, this changesto dark green, and soon afterwards to jight green;and at the same time a thick froth appears on thesurface, indicating the termination of the reaction.The oil is now examined by taking out a smallportion and allowing it to Settle, and if not suf-ficiently bleached an additional portion of thebleaching mixture is added.
After complete decoloration, which is effected infrom ten to fifteen minutes, the oil is permitted toremain undisturbed for about half an hour, so as toallow the deposition of the aqueous solution ofchloride of chromium, sulphate of potash, and otherforeign matters, after which the clear oil is drawnoff into a wooden vat, mixed with a little freshwater, and again heated for a short time by meansof steam. After being once more allowed to restto deposit water, &c., the oil is fit for use.
As already mentioned, the decoloration is effectedin this process by the agency of nascent oxygen.When the solution of bichromate of potash andhydrochloric acid are mixed, the acid of the bichro-mate is liberated, the oxygen of the potash seizesthe hydrogen of the acid, forming water, and thechlorine unites with the potassium to producechloride of potassium, as represented in the annexedequation:—
Bichromate of Hydrochloric Chloride of , Chromic
Potash. Acid. Potassium. Water. Acid.
K 2 Cr0 4 ,Cr0 3 + 2HC1 = 2KC1 + H a O + 2Cr0 3 .
After this decomposition, the mixture, containingan excess of hydrochloric acid, is added to themelted oil; and on coming in contact with theorganic matter, a further change takes place betweenthe hydrochloric and chromic acids. The latter isreduced to chromic oxide, Cr 2 0 3 , and this with